WO2010140171A1

WO2010140171A1 - Solid-state plant growth lighting device and a method for cooling same

Info

Publication number: WO2010140171A1
Application number: PCT/IS2010/000008
Authority: WO
Inventors: Asbjorn Elias Torfason
Original assignee: Asbjorn Elias Torfason
Priority date: 2009-06-02
Filing date: 2010-06-02
Publication date: 2010-12-09

Abstract

This present invention relates to the field of growing plants in a greenhouse or a closed environment. More particularly, it relates to a solid-state plant growth lighting device and a method for cooling LEDs in said lighting device. In one embodiment of the present invention the plant growth lighting device is suitable for mounting in horizontal configuration to provide top lighting for plants. In another embodiment of the present invention the plant growth lighting device is suitable for mounting in vertical configuration to provide inter lighting for plants.

Description

SOLID-STATE PLANT GROWTH LIGHTING DEVICE AND A METHOD FOR COOLING SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

This present invention relates to the field of growing plants in a greenhouse and a closed environment. More particularly, it relates to a solid-state plant growth lighting device and a method for cooling same.

In addition, plants described herein include vegetables, fruits, mushrooms and microalgae etc.

2. Description of the Related Art

The use of artificial lighting systems to enhance growth of plants in greenhouses have been known for decades. Majority of the lighting systems in use relay on high pressure sodium (HPS) or metal halide (MH) lamps for commercial plant production. Unfortunately, these lamps have high energy consumption and produce waste heat which can increase evaporation from the growing media and the transpiration rate of the plants.

In recent years there has been considerable interest in using light emitting diodes (LEDs) in the 600-700 nm red spectrum range, supplemented with LEDs in the 400-500 nm blue spectrum range, as a lighting source to enhance plant growth in greenhouses and closed environment. The advantage of using LEDs is that they are small and light, they have a very long life expectancy, up to 100.000 hours and they have highly efficient conversion of electricity to light, thus minimizing heat generation.

While LEDs offer benefits such as long life, durability and high efficiency, the lifetime of LEDs may be significantly shortened without proper thermal management. The operating lifetime of a LED is directly linked to the operating current and the junction temperature of the LED during operation. Unlike traditional light bulbs, LEDs do not instantly fail. Instead, their light output gradually drecreases with time. LEDs have thermal limits similar to other solid-state devices and can survive junction temperatures as high as 150⁰C. However, the LED operating juntion temperature must be kept much lower to attain a satisfactory lumen maintenance, i.e. the time it takes for the LED light output, measured in lumens, to decrease to 70% of the original output. For example, a typical high brightness LED might have a lumen maintenance of 70% at 50,000 hours when operated at junction temperature of 85°C. Therefore, the higher the operating junction temperature the shorter the LED life expectancy. For example, an LED consistently operated at its maximum junction temperature will have its lifetime reduced to a few thousand hours.

LEDs are available in different packages and lens options for general lighting applications and other applications. It is now possible to purchase IW, 3W, 5W and higher rated high brightness LED emitters in different packages for various applications. Although relatively small, these LEDs require sufficient cooling to attain a satisfactory lumen maintenance. To achieve satisfactory LED reliability and lumen maintenance, the LED should be driven at its binning current (or lower) and be supported by an adequate thermal management system.

There have been several attempts to solve these thermal issues described above. For example European Patent No. EP1933602A1 discloses a lighting system for cultivating plants that has hollow carrier in the form of a tube, with several LEDs inside it. The backs of the LEDs are in the wall of the carrier and cooled by water flowing through the carrier. Furthermore the LEDs are provided with pegs, which after attachement of the LEDs on the assembly blocks protrude through the wall of the carrier into the flow path of the coolant through the carrier. The disclosure makes general statements regarding attachment of LEDs but it gives no teaching or instructions as to how the attachment should be made. Furthermore, the disclosure does not provide sufficient measures to prevent water leakage or corrosion of the pegs.

WO2008/010121A2 discloses a cooling system and a cooling method enabling the use of LEDs mounted on a heat sink for illuminating plants placed in a greenhouse environment. Furthermore the cooling system is provided with at least one pipe having an incoming end and an outgoing end through which ambient air coming from outside the greenhouse is guided. This design uses ambient air cooling method with unreliable fluctuating temperatures which if high enough will reduce the operating lifetime of the LEDs. U.S. Pat. No. 2009/0039752A1 discloses a lightning device for stimulating plant growth. The lightning device has a LED lighting source which is in contact with a cooling medium such as glycol, alcohol, CO₂ or air. This design has insuficcient thermal dissipation path between the LEDs and the cooling pipe, therefore unable to support cooling of multiple LEDs.

SUMMARY OF THE INVENTION

Accordingly, it is the general object of the present invention to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide a solid-state plant growth lighting device with improved thermal management.

The present invention relates to a solid-state plant growth lighting device and a method for thermal management of LEDs in said lighting device. The plant growth lighting device includes a cooling structure and end fittings preferably made from, but not limited to, aluminum. The cooling structure is anodized for improved corrosion resistance and has at least one mounting surface for attaching said LEDs. A coolant flow chamber within the cooling structure comprising a plurality of fins of appropriate size and spacing provides a thermal transfer bridge between said LEDs and the coolant liquid flowing through said coolant flow chamber and end fittings. The coolant liquid is preferably water and may include anti-freeze, anti-corrosive and anti-microbial additives. The anti-microbial additives may possess anti-bacterial, anti-fungal, anti-algal or other anti-microbial activity. The plant growth lighting device is enclosed in a glass, acrylic or PC tubular cover for protecting the LEDs from water and moisture.

In one embodiment of the present invention a plant growth lighting device is shown in a horizontal configuration, namely a plant growth top lighting device for plant cultivation. In this configuration, one or more metal core printed circuit boards (MCPCBs) with one or more LEDs, are attached to a cooling structure providing cooling for the LEDs.

In another embodiment of the present invention the plant growth lighting device is shown in a vertical configuration, namely plant growth inter lighting device for plant cultivation. In this configuration, number of MCPCBs with one or more LEDs, are attached to a cooling structure providing cooling for the LEDs.

Another object of the present invention is to simultaneously protect the interior and exterior surfaces of the extruded aluminum cooling structure and end fittings from the effects of spontaneous corrosion as well as to provide an improved corrosion prevention method which is easy to apply and economical to maintain.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the objects, advantages, and principles of the present invention. In the drawings,

FIG. 1 is a perspective side view of the horizontal solid-state plant growth top lighting device in accordance with a first embodiment of the present invention;

FIG. 2a is a cross-sectional view of an axially grooved octagonal cooling structure for a vertical inter lighting device having the plurality of different sized fins on the surface inside the octagonal coolant flow chamber thereof in accordance with a second embodiment of the present invention;

FIG. 2b is a cross-sectional view of an axially grooved hexagonal cooling structure for a vertical inter lightning device having the plurality of different sized fins on the surface inside the hexagonal coolant flow chamber thereof in accordance with a third embodiment of the present invention; FIG. 2c is a cross-sectional view of a axially grooved pentagonal cooling structure for a vertical inter lighting device having the plurality of different sized fins on the surface inside the pentagonal coolant flow chamber thereof in accordance with a fourth embodiment of the present invention;

FIG. 2d is a cross-sectional view of an axially grooved half circular or less cooling structure for a horizontal top lighting device having the plurality of mostly similar sized fins on the straight surface inside the coolant flow chamber thereof in accordance with a fifth embodiment of the present invention;

FIG. 2e is a cross-sectional view of an axially grooved circular and partial octagonal cooling structure for a horizontal top lighting device of FIG. 1 having the plurality of different sized fins on the surface inside the partial octagonal coolant flow chamber thereof in accordance with an embodiment of the present invention;

FIG. 2f is a cross-sectional view of an axially grooved half circular and a half hexagonal cooling structure for a horizontal top lighting device having the plurality of different sized fins on the surface inside the partial hexagonal coolant flow chamber thereof in accordance with a sixth embodiment of the present invention;

FIG. 3 is a cross-sectional view of the axially grooved octagonal cooling structure of FIG. 2a taken along line Ill-Ill thereof in accordance with an embodiment of the present invention;

FIG. 4a is an enlarged partial cross-sectional view showing a rectangular form of the axially extending fins on the surface inside the coolant flow chamber of the cooling structure in accordance with a seventh embodiment of the present invention;

FIG. 4b is an enlarged partial cross-sectional view showing a rounded rectangular form of the axially extending fins on the surface inside the coolant flow chamber of the cooling structure in accordance with an eigth embodiment of the present invention; and

FIG. 4c is an enlarged partial cross-sectional view showing a circular form of the axially extending fins on the surface inside the coolant flow chamber of the cooling structure in accordance with a ninth embodiment of the present invention; FIG. 5 is a cross-sectional view of the horizontal solid-state plant growth top lighting device in accordance with an embodiment of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

After reading this description it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, all the various embodiments of the present invention will not be described herein. It is understood that the embodiments presented here are presented by way of an example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention as set forth below.

With reference to FIG. 1, a first embodiment of the present invention, there is shown a horizontally mounted solid-state plant growth top lighting device 1 consisting of an axially grooved cooling structure 2 and end fittings 3 and 4 screwed together or welded to both ends of the cooling structure 2. The cooling structure 2 is preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6. The cooling structure 2 is preferably anodized for improved corrosion resistance. Both end fittings 3 and 4 may have lugs 5 and 6 for hanging the top lighting device 1 to a greenhouse structure or other overhead frame using, but not limited to, stainless steel wire ropes 7 and 8 fastened to the lugs 5 and 6 using, but not limited to, wire rope sockets 9 and 10. Light emitting diodes (LEDs) 11 are mounted on metal core printed circuit boards (MCPCBs) 12 which in turn are attached to the flat surfaces underneath the cooling structure 2 using a thermal conductive adhesive agent. For protecting the LEDs from water and moisture, the plant growth top lighting device 1 is enclosed preferably in, but not limited to, glass, acrylic (PMMA) or PolyCarbonate (PC) transparent tubular cover 13 and sealed at both ends with suitable water and UV resistant sealant 14 and 15. A power connection, such as power cable 16 extending from one end of the MCPCB passes through a hole in the tubular cover 13. The top lighting device 1 is cooled by means of coolant liquid flow supplied by a hose 17 connected to the end fitting 4 compatible with, but not limited to, standardized inlet connector 18 of a quick connect/release type. Coolant liquid flow exit is by hose 19 connected to the end fitting 3 compatible with, but not limited to, standardized outlet connector 20 of a quick connect/release type.

Referring still to FIG. 1, it may be seen that the connecting method for the coolant liquid supply may be modified in accordance with the principles of the present invention. The connecting method may vary depending on cooling requirements of the LEDs 11 used and circumstances in the greenhouse or the closed environment. In one embodiment of the present invention, it may be appropriate to use anodized aluminum die cast barbed hose end fittings (not shown) and hose clamps to prevent leaks. In another embodiment of the present invention, it may be appropriate to use anodized aluminum die cast screw end fittings (not shown) and anodized aluminum pipes with union nuts (not shown) for the coolant liquid supply. In yet another embodiment of the present invention, it may be advantageous to teflon coat the end fittings 3 and 4 and the coolant flow chamber 24 surface inside the cooling structure 2 to improve the corrosion resistance further and to reduce friction of the coolant liquid flowing through the top lighting device 1. The addition of a thin teflon coating on the surface inside the cooling structure 2 produces no significant deterioration in heat transfer efficiency. However, it will be recognized that other types of materials may be utilized to fabricate the top lighting device 1, with such materials preferably including a low-friction coating applied thereto.

With reference to FIG. 2a, a second embodiment of the present invention, there is shown a cross-sectional view of an axially grooved octagonal cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, for a vertical inter lighting device, having the plurality of different sized fins 21 and grooves 22 on the surface inside the octagonal coolant flow chamber 24 thereof. The corner groove 23 formed by adjacent fins is kept open by setting the hight of the corner fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge between the LEDs 11 and the coolant liquid flowing through said coolant flow chamber 24.

Referring still to FIG. 2a, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the sides of the octagonal cooling structure 2 using a thermal conductive adhesive agent. With reference to FIG. 2b, a third embodiment of the present invention, there is shown a cross-sectional view of an axially grooved hexagonal cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, for a vertical inter lighting device, having the plurality of different sized fins 21 and grooves 22 on the surface inside the hexagonal coolant flow chamber 24 thereof. The corner groove 23 formed by adjacent fins is kept open by setting the hight of the corner fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge between the LEDs 11 and the coolant liquid flowing through said coolant flow chamber 24.

Referring still to FIG. 2b, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the sides of the hexagonal cooling structure 2 using a thermal conductive adhesive agent.

With reference to FIG. 2c, a fourth embodiment of the present invention, there is shown a cross-sectional view of an axially grooved pentagonal cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, for a vertical inter lighting device, having the plurality of different sized fins 21 and grooves 22 on the surface inside the pentagonal coolant flow chamber 24 thereof. The corner groove 23 formed by adjacent fins is kept open by setting the hight of the corner fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge between the LEDs 11 and the coolant liquid flowing through said coolant flow chamber 24.

Referring still to FIG. 2c, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the sides of the pentagonal cooling structure 2 using a thermal conductive adhesive agent.

With reference to FIG. 2d, a fifth embodiment of the present invention, there is shown a cross-sectional view of an axially grooved half-circular or less cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, for a horizontal top lighting device, having the plurality of mostly similar sized fins 21 and grooves 22 on the straight surface inside the coolant flow chamber 24 thereof. The corner groove 23 formed by the corner fin and the circular arc is kept open by setting the hight of the corner fin or fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge between the LEDs 11 and the coolant liquid flowing through said coolant flow chamber 24.

Referring still to FIG. 2d, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the flat surface underneath the half-circular or less cooling structure 2 using a thermal conductive adhesive agent.

With reference to FIG. 2e, an embodiment of the present invention, there is shown a cross- sectional view of an axially grooved circular and partial octagonal cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, for the horizontal top lighting device 1 of FIG. 1, having the plurality of mostly similar sized fins 21 and grooves 22 on the surface inside the partial octagonal coolant flow chamber 24 thereof. The corner groove 23 formed by adjacent fins is kept open by setting the hight of the corner fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge between the LEDs 11 and the coolant liquid flowing through said coolant flow chamber 24.

Referring still to FIG. 2e, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the flat surfaces of the partial octagonal cooling structure 2 using a thermal conductive adhesive agent.

With reference to FIG. 2f, a sixth embodiment of the present invention, there is shown a cross-sectional view of an axially grooved half circular and a half hexagonal cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, for a horizontal top lighting device, having the plurality of mostly similar sized fins 21 and grooves 22 on the surface inside the half hexagonal coolant flow chamber 24 thereof. The corner groove 23 formed by adjacent fins is kept open by setting the hight of the corner fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge between the LEDs 11 and the coolant liquid flowing through said coolant flow chamber 24.

Referring still to FIG. 2f, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the sides of the half hexagonal cooling structure 2 using a thermal conductive adhesive agent. With reference to FIG. 3 there is shown a cross-sectional view of the axially grooved octagonal cooling structure 2, preferably made from, but not limited to, extruded aluminum alloy such as 6061-T6, of FIG. 2a taken along line IH-IH thereof according to the present invention. In this embodiment, the cooling structure 2 is preferably of a pentagonal, hexagonal or octagonal shape. The example illustrated in FIG. 3 shows a vertical plant growth inter lighting device 1 with high brightness LEDs 11 mounted to MCPCBs 26, which in turn are attached to the sides of the octagonal cooling structure 2 using a thermal conductive agent. During operation the heat generated by the LEDs 11 is transferred to the coolant liquid, that is continously flowing through the coolant flow chamber 24 from the input side 52 to the output side 53 or vise versa, by means of heat transfer through the MCPCBs 26 which have high heat transfer capability and then through the cooling structure 2 to the fins 21 where the heat is transferred to the flow of coolant liquid and then removed. The present invention has advantage over prior art, as there are number of fins 21 present, of appropriate size and spacing, that increase the surface area of the coolant flow chamber 24, without trapping the coolant liquid in the corners, accelerating the heat dissipation and therby optimizing the thermal transfer. As the increased surface area of the coolant flow chamber 24 accelerates heat dissipation of the aluminum cooling structure 2, it is possible to effectively cool the LEDs 11 to maintain their expected light output, life, and colour.

Referring still to FIG. 3 there is an installation method (not shown) using, but not limited to, two end fittings with two lugs 180° apart per fitting for hanging the vertical inter lighting device 1 to a greenhouse structure, other overhead frame or to another vertical plant growth inter lighting device 1 using, but not limited to, stainless steel wire ropes fastened to the lugs using wire rope sockets. Furthermore, the inter lighting device 1 is cooled by means of coolant liquid supplied, not limited to but preferably, by a hose (not shown) connected to an end fitting (not shown) on the input side 52 using, but not limited to, standardized inlet connector (not shown) of a quick connect/release type. Coolant liquid flow exit is, not limited to but preferably, by a hose (not shown) connected to an end fitting (not shown) on the output side 53 using, but not limited to, standardized outlet connector (not shown) of a quick connect/release type. The end fittings are preferably made from, but not limited to, aluminum. The connecting method may vary depending on cooling requirements of the LEDs 11 used and circumstances in the greenhouse or the closed environment. In one embodiment of the present invention, it may be appropriate to use anodized aluminum die cast barbed hose end fittings (not shown) and hose clamps (not shown) to prevent leaks. In another embodiment of the present invention, it may be appropriate to use anodized aluminum die cast screw end fittings (not shown) and anodized aluminum pipes with union nuts (not shown) for the coolant liquid supply. In yet another embodiment of the present invention, it may be advantageous to teflon coat the aluminum end fittings (not shown) and the surface inside the coolant flow chamber 24 of the cooling structure 2 to improve the corrosion resistance further and to reduce friction of the coolant liquid flowing through the vertical inter lighting device 1. The addition of a thin teflon coating to the surface inside the coolant flow chamber 24 produces no significant deterioration in heat transfer efficiency. However, it will be recognized that other types of materials may be utilized to fabricate the inter lighting device 1, with such materials preferably including a low-friction coating applied thereto.

With reference to FIG. 4a, an embodiment of the present invention, there is shown an enlarged partial cross-sectional view of a rectangular form of axially extending fins 21 on the surface inside of an axially grooved cooling structure 2. In this embodiment, there is shown a portion, preferably of pentagonal, hexagonal or octagonal shaped extruded cooling structure 2 preferably made from, but not limited to, aluminum alloy such as 6061-T6. To provide optimal heat dissipation and thermal transfer bridge from the LEDs to the surface inside the coolant flow chamber 24 of the cooling structure 2, it is important that the adjacent fins 21 located at the inside corners are of appropriate size and spacing so the flowing coolant liquid can easily enter and exit the cooling grooves 22 and 23. For this reason and according to the present invention, the width W of the fins 21 is defined from 0.4 to 3.0 mm, and the height H of the fins 21 is defined from 1.0 to 11.0 mm, and the groove width, determined by the spacing S between fins 21 is defined from 0.4 to 4.0 mm, and the distance L₁ between adjacent fins 21 in the second innermost corner is defined >3.0 W mm, and the distance L₂ between adjacent fins 21 in the innermost corner is defined >1.0 W mm. The choice of measurements in mm to be used depends on the size of the plant growth lighting device, number of LEDs used, and the power rating of the LEDs. It must also be realized that the temperature of the flowing coolant liquid must be sufficiently cold and constant to effectively cool the LEDs. However, too cold coolant liquid could lead to condensation on outside of the cooling structure 2 that could lead to electrical shorts and corrosion.

With reference to FIG. 4b, a seventh embodiment of the present invention, there is shown an enlarged partial cross-sectional view of a rounded rectangular form of axially extending fins 21 on the surface inside of an axially grooved cooling structure 2. In this embodiment, there is shown a portion, preferably of pentagonal, hexagonal or octagonal shaped extruded cooling structure 2 preferably made from, but not limited to, aluminum alloy such as 6061-T6. To provide optimal heat dissipation and thermal transfer bridge from the LEDs to the surface inside the coolant flow chamber 24 of the cooling structure 2, it is important that the adjacent fins 21 located at the inside corners are of appropriate size and spacing so the flowing coolant liquid can easily enter and exit the cooling grooves 22 and 23. For this reason and according to the present invention, the width W of the fins 21 is defined from 0.4 to 3.0 mm, and the height H of the fins 21 is defined from 1.0 to 11.0 mm, and the groove width, determined by the spacing S between fins 21 is defined from 0.4 to 4.0 mm, and the distance Li between adjacent fins 21 in the second innermost corner is defined >3.0 W mm, and the distance L₂ between adjacent fins 21 in the innermost corner is defined >1.0 W mm. The choice of measurements in mm to be used depends on the size of the plant growth lighting device, number of LEDs used, and the power rating of the LEDs. It must also be realized that the temperature of the flowing coolant liquid must be sufficiently cold and constant to effectively cool the LEDs. However, too cold coolant liquid could lead to condensation on outside of the cooling structure 2 that could lead to electrical shorts and corrosion.

With reference to FIG. 4c, an eight embodiment of the present invention, there is shown an enlarged partial cross-sectional view of a circular form of axially extending fins 21 on the surface inside of an axially grooved cooling structure 2. In this embodiment, there is shown a portion, preferably of pentagonal, hexagonal or octagonal shaped extruded cooling structure 2 preferably made from, but not limited to, aluminum alloy such as 6061-T6. To provide optimal heat dissipation and thermal transfer bridge from the LEDs to the surface inside the coolant flow chamber 24 of the cooling structure 2, it is important that the adjacent fins 21 located at the inside corners are of appropriate size and spacing so the flowing coolant liquid can easily enter and exit the cooling grooves 22 and 23. For this reason and according to the present invention, the width W of the fins 21 is defined from 0.4 to 3.0 mm, and the height H of the fins 21 is defined from 1.0 to 11.0 mm, and the groove width, determined by the spacing S between fins 21 is defined from 0.4 to 4.0 mm, and the distance L₁ between adjacent fins 21 in the second innermost corner is defined >3.0 W mm and the distance L₂ between adjacent fins 21 in the innermost corner is defined >1.0 W mm. The choice of measurements in mm to be used depends on the size of the plant growth lighting device, number of LEDs used, and the power rating of the LEDs. It must also be realized that the temperature of the flowing coolant liquid must be sufficiently cold and constant to effectively cool the LEDs. However, too cold coolant liquid could lead to condensation on outside of the cooling structure 2 that could lead to electrical shorts and corrosion.

With reference to FIG. 5, still another embodiment of the present invention, there is shown a cross-sectional view of an axially grooved half-circular or less aluminum cooling structure 2 for a horizontal top lighting device, having plurality of mostly similar sized fins 21 and grooves 22 on the straight surface inside the coolant flow chamber 24 thereof. The corner groove 23 formed by the corner fin and the circular arc is kept open by setting the hight of the corner fin or fins so to prevent trapping the flow of the coolant liquid in the corners, thus providing more efficient heat transfer bridge from the LEDs 11 to the surface inside the coolant flow chamber 24 of the cooling structure 2.

Referring still to FIG. 5, the LEDs 11 are mounted on MCPCBs 26 which in turn are attached to the flat surface underneath the half-circular or less extruded aluminum cooling structure 2 using a thermal conductive adhesive agent. Furthermore, the LEDs 11 and their electrical connection leads are protected by dielectric encapsulant such as silicone or epoxy 75. The cooling structure 2 can be fitted with optional transparent protective cover 13 preferably made from, but not limited to, glass, acrylic (PMMA) or PolyCarbonate (PC) with optional diffusing properties on the inside surface 77. Furthermore, on top of the cooling structure 2 there are flanges 78 to ease the mounting of the horizontal top lighting device to different sized pipes 79. Furthermore, there are threaded extruded holes 80 for fastening the end fittings (not shown) preferably made from, but not limited to, aluminum, plastic PVC or like, to both ends of the cooling structure 2. Extruded screw holes 80 advantageously permit long lengths of the extruded cooling structure 2 to be fabricated, which can then be cut to specified lengths, each cut length having screw holes 80 immediately available.

In the present invention, the LEDs 11 used for growing plants in a greenhouse or a closed environment preferably emit light in a red spectrum range of 600-700 nm, supplemented with light emitted in a blue spectrum range of 400-500 nm. The red and blue wavelengths of the light spectrum are the most valuable energy resources for plant life. It should be noted that light emitted in the 500-600 nm are less important in photosynthesis than red spectral range for certain plants. Furthermore, the present invention may include LEDs 11 in the infra-red spectral range of 700-750 nm for enhancement of flowering and stem elongation. In the present invention, the LEDs 11 are preferably operated from a direct current (DC) source such as AC/DC converter (not shown). In another embodiment of the present invention, the LEDs 11 may be flashed with pulsed direct current (DC) in the frequency range of 10 hz to 2 Mhz for energy saving reasons or for improving photonic flux tolerance of plants. In another embodiment of the present invention, so-called alternative current (AC) LEDs may be used instead of DC LEDs 11. The advantage of AC LEDs is that they do not require a direct current (DC) source such as AC/DC converter, instead they can be operated directly from AC mains supply, therefore reducing the number of components, increasing the efficiency and reliability of the plant growth lighting device 1 of FIG. 1 and FIG. 3.

It is understood that the drawings show an exemplification given only as a practical demonstration of the invention. The drawings may vary in forms and dispositions without exceeding the scope of the idea on which the present invention is based. These embodiments are not meant as limitations of the invention, but merely exemplary descriptions of the invention with regard to certain specific embodiments. Indeed, different adaptations may be apparent to those skilled in the art without departing from the scope of the annexed claims.

Claims

What is claimed is:

1. A solid-state lighting device (1) comprising: at least one Light Emitting Diode (LED) (11) for generating light; a power connection (16) for electrically connecting to said at least one LED (11); a cooling structure (2), having at least one mounting surface where said at least one LED (11) is mounted and at least one coolant flow chamber (24); a coolant end fittings (3) and (4), providing flow of coolant liquid into and out of said coolant flow chamber (24); said coolant flow chamber (24) with inside surface comprising a plurality of fins (21) and grooves (22) providing a thermal transfer bridge between said LED (11) and the coolant liquid flowing within said coolant flow chamber (24) and a protective cover (13) enclosing at least said at least one LED (11).

2. A solid-state lighting device (1) according to claim 1, comprising LEDs, in a red spectrum range of 600-700 nm.

3. A solid-state lighting device (1) according to claim 1 or 2, comprising LEDs, in a blue spectrum range of 400-500 nm.

4. A solid-state lighting device (1) according to claim 1, 2, or 3, comprising LEDs, in a infra-red spectrum range of 700-750 nm.

5. A solid-state lighting device (1) according to any of the claims 1, 2, 3 or 4, comprising LEDs (11) operated from a direct current (DC) source.

6. A solid-state lighting device (1) according to any of the claims 1-5, comprising LEDs (11) flashed with pulsed direct current (DC) in the frequency range of 10 hz to 2 Mhz.

7. A solid-state lighting device (1) according to any of the claims 1-6, comprising alternative current (AC) LEDs (11) operated directly from AC mains supply.

8. A solid-state lighting device (1) according to claim 1, wherein said end fittings (3) and (4) are of a quick connect/release type.

9. A solid-state lighting device (1) according to claim 1, wherein said end fittings (3) and (4) are die cast barbed hose end fittings.

10. A solid-state lighting device (1) according claim 1, wherein said end fittings (3) and (4) are plastic PVC hose end fittings.

11. A solid-state lighting device (1) according claim 1, wherein said end fittings (3) and

(4) are screw end fittings.

12. A solid-state lighting device (1) according to claim 1, wherein said cooling structure (2) dissipates heat generated by said LEDs (11), wherein said fins (21) on the surface inside the coolant flow chamber (24) of said cooling structure (2) have rectangular form, wherein the width W of said fins (21) is defined from 0.4 to 3.0 mm, and the height H of said fins (21) is defined from 1.0 to 11.0 mm, and the groove width determined by a spacing S between said fins (21) is defined from 0.4 to 4.0 mm, and the distance Li between said fins (21) in said second innermost corner is defined >3.0 W mm and the distance L₂ between said fins (21) in said innermost corner is defined

>1.0 W mm.

13. A solid-state lighting device (1) according to claim 1, wherein said cooling structure (2) dissipates heat generated by said LEDs (11), wherein said fins (21) on the surface inside the coolant flow chamber (24) of said cooling structure (2) have rounded rectangular form, wherein the width W of said fins (21) is defined from 0.4 to 3.0 mm and the height H of said fins (21) is defined from 1.0 to 11.0 mm and the groove width, determined by the spacing S between said fins (21), is defined from 0.4 to 4.0 mm and the distance Li between said fins (21) in said second innermost corner is defined >3.0 W mm and the distance L₂ between said fins (21) in said innermost corner is defined >1.0 W mm.

14. A solid-state lighting device (1) according to claim 1, wherein said cooling structure (2) dissipates heat generated by said LEDs (11), wherein said fins (21) on the surface inside the coolant flow chamber (24) of said cooling structure (2) have circular form, wherein the width W of said fins (21) is defined from 0.4 to 3.0 mm and the height H of said fins (21) is defined from 1.0 to 11.0 mm and the groove width, determined by the spacing S between said fins (21), is defined from 0.4 to 4.0 mm and the distance L₁ between said fins (21) in said second innermost corner is defined >3.0 W mm and the distance L₂ between said fins (21) in said innermost corner is defined >1.0 W mm.

15. A solid-state lighting device (1) according to any of the claims 1-14, wherein cooling structure (2) can be fitted with transparent protective cover (13) with optional diffusing properties on the inside surface (77).

16. A solid-state lighting device (1) according to any of the claims 1-15, wherein said lighting device (1) is in a horizontal top lighting configuration.

17. A solid-state lighting device (1) according to any of the claims 1-15, wherein said lighting device (1) is in a vertical inter lighting configuration.